Conventionally, in mobile communication, since reception waves in multipath propagation vary in propagation path length, multipath waves with different propagation delay times interfere with each other. A CDMA receiving apparatus band-spreads information data by using a high-rate spreading code with a period shorter than a propagation time, and hence can separate/extract the respective multipath waves with different propagation delay times.
This CDMA receiving apparatus generates a power delay profile by de-spreading a pilot signal while shifting the time, searches for effective paths (path search) from the generated power delay profile, and performs in-phase combining (RAKE combining) with respect to the paths. This makes it possible to obtain a diversity effect and improve the reception characteristics.
A path search is the processing of gradually changing the timing of a spreading code by which a reception signal is multiplied, measuring correlation values at the respective timings, and determining the timings of several paths with large correlation values.
In general, path search processing uses a common pilot channel (CPICH) with transmission power relatively higher than that of an individual channel.
In addition, a power delay profile is generally generated by using a common pilot channel with transmission power higher than an individual channel (see, for example, reference 1 (Japanese Patent Laid-Open No. 9-181704) and reference 2 (Japanese Patent Laid-Open No. 2004-120643)).
In addition, as de-spreading processing for pilot signals, there has also been proposed a method of calculating correlations with reception signals while switching a spreading code for a common pilot channel and a spreading code for an individual channel (see, for example, reference 3 (Japanese Patent Laid-Open No. 2004-289191).
Note that as the reception quality on an individual channel deteriorates, transmission power control increases the transmission power of a base station. No transmission power control is performed on the common pilot channel.